NOTE: A plug with a low heat range number is a cold plug that quickly dissipates heat to the engine block and cooling system, while a high heat range is a hot plug that retains heat. By properly selecting the heat range of the plug, it ensures that the plug will operate between the plug’s designed operating range of 500-900 degrees Celsius. In this range, the spark plug will be self-cleaning, yet will not be hot enough to pre-ignite the air/fuel mixture